1. Field of the Invention
The present invention relates to a motor driving apparatus for generating a large motor output torque.
2. Description of the Related Art
In order to drivingly control a large-capacity motor using an inverter unit, the inverter unit needs to be a large-capacity one. However, due to restrictions on components of an inverter unit, it is difficult to construct a single large-capacity inverter unit. Instead of using a single large-capacity inverter unit, a method is employed in which a large-capacity motor is drive-controlled by obtaining a large output from a plurality of small-capacity inverter units connected in parallel, equivalently.
FIG. 8 is a block diagram showing a control method conventionally employed in controlling a large-capacity motor using a plurality of inverter units.
A motor control unit 1 generates a plurality of motor driving commands and feeds them to a plurality (four in FIG. 8) of inverter units IV1 to IV4 arranged in parallel, individually, to thereby perform PWM control or the like on the inverter units IV1 to IV4 so that the inverter units IV1 to IV4 will drive a large-capacity motor 2 simultaneously. Thus, the inverter units IV1 to IV4 put together can drive-control the large-capacity motor 2, although they are each small in capacity.
Further, as a method of using two motors to drive a large-size movable piece for which acceleration/deceleration-control or the like by a single motor is difficult, a tandem control method is known to the public, in which two motors are driven with a single torque command (current command) generated by a motor control unit (see JP 8-16246A).
In order to feed motor driving commands to a plurality of inverter units individually, a motor control unit needs to generate the same number of motor driving commands as the inverter units. During this processing, a plurality of motor driving command generating parts are used exclusively for driving a single motor. This produces a problem that when other motors should be drive-controlled by the motor control unit, the number of other motors that can be drive-controlled are restricted.